1. Field of the Invention
The present invention relates generally to carbon brushes for use in motors, and more particularly to a wear-premonitory carbon brush holder.
2. Description of the Related Art
As shown in FIG. 1, a conventional carbon brush holder 1 includes a holder body 11 for accommodating a spring A and a carbon brush B. The spring A has an end contacting against an internal end of the holder body 11 and the other end contacting against an end of the carbon brush B; meanwhile, the carbon brush B is pushed by the spring A to contact against the rotor C of the motor and then transfers the electric current to the rotor C to drive the rotor C to rotate.
Because the friction generated between the carbon brush B and the rotor C wears the carbon brush B, the carbon brush B needs the resilience generated by the spring A to keep contacting against the rotor C. However, the resilience of the spring A will be gradually reduced when the spring A is self-extended along with the wear of the carbon brush B. When the carbon brush B is worn to a certain degree, the spring A fails to provide sufficient resilience to enable the carbon brush B to keep contacting against the rotor C, such that a gap will be formed between the carbon brush B and the rotor C to incur imperfect contact therebetween to further generate arc sparks. Thus, when the motor mounted with the carbon brush holder 1 is operated, the operator has to frequently check the wear degree of the carbon brush B and replace the carbon brush B when the carbon brush B is worn to a certain degree.
As shown in FIG. 2, another conventional carbon brush holder 2 is different from the aforementioned carbon brush holder 1 by that the spring D is a constant-force spring that generates balanced constant resilience to avoid the generation of the aforementioned arc sparks; however, the operator still has to frequently check the wear degree of the carbon brush 2.